The Network Time Protocol (NTP) is used to synchronize the time of a computer client or server to another server or reference time source, such as a radio or satellite receiver or modem. It provides client accuracies typically within a millisecond on LANs and up to a few tens of milliseconds on WANs relative to a primary server synchronized to Coordinated Universal Time (UTC) via a Global Positioning Service (GPS) receiver, for example.

Dateutils are a bunch of tools that revolve around fiddling with dates and times in the command line, with a strong focus on use cases that arise when dealing with large amounts of financial data. Their target market is shell scripts that need date calculations or calendar conversions, and as such they are highly pipe-able and modeled after their well-known cousins (e.g. dtest vs. test, or dgrep vs. grep).

SquidTL allows proxy administrators to manage proxy users: define how much time users can spend on a specific Web site, block sites, limit total time users can spend on the Web daily, and watch users' activity. For example, you can limit the use of Facebook or other social networks with per-user rules or IP. It has a small memory footprint and very fast execution. Management can be done with a smart Web-based administration GUI.

timekpr will track and control the computer usage of your user accounts. You can limit their daily usage based on a timed access duration and configure periods of day when they can or cannot log in. With this application, administrators can limit account login time duration or account access hours. It has support for GNOME, KDE, and XFCE and uses time and access Linux PAM modules. It is currently limited to Ubuntu only.

daytime is a program that can get the current time from "daytime" (RFC-867), "time" (rfc-868), "nist daytime", or HTTP servers. It only uses the TCP versions of these protocols. It can set the system or hardware clocks from the retrieved time.

python-chrono is a Python module for simple and convenient date/time handling, including parsing, arithmetic, comparison, formatting, and calendar functionality. It supports both the ISO and US calendars, and dates/times in ISO, US, and European formats.

tstime is a command that is similar to the time(1) command, but in addition to the runtime, it also prints the highwater memory usage (RSS+VMEM) of the controlled process. tsmon is a command that prints the runtime/highwater memory usage of every process that exits on the system until the tsmon is quit. These programs use the taskstats delay accounting interface of the Linux 2.6 kernel.

Gameclock is a fairly simple application designed to track the time spent thinking by the players during a chess game. Various clock engines are available (speed chess, fisher chess, board games, or hourglass). The graphical interface is keyboard-driven and is intended to be minimal and simple. The code is made to be extensible to other game types.